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    ABSTRACT: Fusarium verticillioides is an important pathogen in maize that causes various diseases affecting all stages of plant development worldwide. The fungal pathogen could be seed borne or survive in soil and penetrate the germinating seed. Most F. verticillioides strains produce fumonisins, which are of concern because of their toxicity to animals and possibly humans, and because they enhance virulence against seedlings of some maize genotypes. In this work, we studied the action of fumonisin B1 (FB1) on the activity of maize β-1,3-glucanases involved in plant defense response. In maize embryos, FB1 induced an acidic isoform while suppressing the activity of two basic isoforms. This acidic isoform was induced also with 2,6-dichloroisonicotinic acid, an analog of salicylic acid. Repression of the basic isoforms suggested a direct interaction of the enzymes with the mycotoxin as in vitro experiments showed that pure FB1 inhibited the basic β-1,3-glucanases with an IC(50) of 53 μM. When germinating maize embryos were inoculated with F. verticillioides the same dual effect on β-1,3-glucanase activities that we observed with the pure toxin was reproduced. Similar levels of FB1 were recovered at 24 h germination in maize tissue when they were treated with pure FB1 or inoculated with an FB1-producing strain. These results suggest that β-1,3-glucanases are a relevant physiological target and their modulation by FB1 might contribute to F. verticillioides colonization.
    Planta 11/2011; 235(5):965-78. · 3.38 Impact Factor
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    ABSTRACT: Sphingolipids play an important role in signal transduction pathways that regulate physiological functions and stress responses in eukaryotes. In plants, recent evidence suggests that their metabolic precursors, the long-chain bases (LCBs) act as bioactive molecules in the immune response. Interestingly, the virulence of two unrelated necrotrophic fungi, Fusarium verticillioides and Alternaria alternata, which are pathogens of maize and tomato plants, respectively, depends on the production of sphinganine-analog mycotoxins (SAMs). These metabolites inhibit de novo synthesis of sphingolipids in their hosts causing accumulation of LCBs, which are key regulators of programmed cell death. Therefore, to gain more insight into the role of sphingolipids in plant immunity against SAM-producing necrotrophic fungi, we disrupted sphingolipid metabolism in Nicotiana benthamiana through virus-induced gene silencing (VIGS) of the serine palmitoyltransfersase (SPT). This enzyme catalyzes the first reaction in LCB synthesis. VIGS of SPT profoundly affected N. benthamiana development as well as LCB composition of sphingolipids. While total levels of phytosphingosine decreased, sphinganine and sphingosine levels increased in SPT-silenced plants, compared with control plants. Plant immunity was also affected as silenced plants accumulated salicylic acid (SA), constitutively expressed the SA-inducible NbPR-1 gene and showed increased susceptibility to the necrotroph A. alternata f. sp. lycopersici. In contrast, expression of NbPR-2 and NbPR-3 genes was delayed in silenced plants upon fungal infection. Our results strongly suggest that LCBs modulate the SA-dependent responses and provide a working model of the potential role of SAMs from necrotrophic fungi to disrupt the plant host response to foster colonization.
    Planta 09/2012; · 3.38 Impact Factor
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    ABSTRACT: Erwinia chrysanthemi is a devastating bacterial pathogen in Phalaenopsis amabilis and causes soft-rotting disease by secretion of cell wall-degrading enzymes. However, the molecular mechanisms underlying the interaction of P. amabilis with E. chrysanthemi remain elusive. In this study, early molecular events of the plant in response to the pathogen attack were investigated. The alteration in reactive oxygen species accumulation and peroxidase activity occurred at the site of infection. Subsequently, a systematic sequencing of expressed sequence tags (ESTs) using suppression subtractive hybridization (SSH) was performed to obtain the first global picture of the assembly of genes involved in the pathogenesis. The majority of the SSH clones showed a high identity with genes coding for proteins that have known roles in redox homeostasis, responses to pathogens and metabolism. A notable number of the SSH clones were those encoding WRKY, MYB and basic leucine zipper transcription factors, indicating the stimulation of intracellular signal transduction. An orchid gene encoding trans-2-enoyl-CoA reductase (ECR) was the most abundant transcripts in the EST library. ECR is an enzyme catalyzing the very long chain fatty acids (VLCFAs) biosynthesis, and the full-length cDNA of the ECR gene (PaECR1) was obtained. Functional analysis of PaECR1 was conducted by virus-induced gene silencing to knock down the gene expression in P. amabilis. The PaECR1-silenced plants were more susceptible to E. chrysanthemi infection, implying potential roles for VLCFAs in the pathogenesis. In summary, the pathogen-responsive gene expression profiles facilitated a more comprehensive view of the molecular events that underlie this economically important plant-pathogen interaction.
    Physiologia Plantarum 01/2012; 145(3):406-25. · 3.66 Impact Factor

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